hi sheila,
sorry that your daughter is having some issues and it's coming down to a cf sweat test. The rectal prolapse and loose bowels and weight gain issues are red flags of cf and along with the chest infections, i'd say that the doctors have some good reasons to do the sweat test. If the sweat test comes out negative or borderline i would push for an ambry genetic panel to be done. There are some mutations of the disease that will come out negative or borderline. My boys are all on the high side of borderline, just under the positive mark; however genetics confirmed their diagnosis. Just know that cf is a spectrum disease, meaning that not everbody is affected the same way. Most parents notice the salty tasting skin, however some don't..and that's kind of open to interpretation too...depending on your taste buds. :0) some with cf are pancreatic insuffcient, which leads to malabsorbtion and weight gain issues, there are some that have just respitory issues, or some that have a combination of the the both. I think you are in the right place to get some questions answered and vent your concerns. Hey, and even if your daughter doesn't have cf after all... you'll meet lots of great friendly people in the process.
also, if you can get a copy of David M. Orenstein "cystic fibrosis" a guide for patient and family...that thing is like a cf bible. Very easy to read and lots of topics.
take care and hang in there, i know i had to wait a while till i had a definite diagnosis..the waiting is agonizing...but once you know for sure you find comfort in knowing that you try to help your child and get them the proper treatment.